In this project we intend to study the intrinsic of the cortex. By elucidating the 'wiring diagram' of the cortex, we hope to gain insight into the basic mechanisms of cortical processing. To attain this objective, we will use two main approaches. One is to do intracellular recording and marking of cells that have been functionally characterized, in an in vivo preparation. With this approach, we can describe for a single cell both its receptive field properties and its detailed 3-dimensional structure. This provides information concerning the relationship between cell structure and function, and also shows the detailed intracortical axonal projections of the injected cell. As we accumulate a catalog of injected cells, we will be able to determine the predominant patterns of intracortical projections and from that to develop ideas concerning the mechanism of receptive field construction. The second method is one that should extend the findings of the first, by directly demonstrating the synaptic relationship between particular cell classes. This will be accomplished by recording from and injecting paired cells in an in vitro tissue slice preparation. In this way we can identify and make detailed descriptions of the morphology of cells that are monosynaptically related. This can be related back to the correlation between morphology and function obtained by the in vivo experiments, resulting in a thorough characterization of the inputs to a particular functional class. We will thus be able to describe the steps involved in the interpretation of sensory information within a single cortical area, which shoudl then lead to the eventual understanding of the mechanisms of operation of other cortical areas as well.